For multi-connected air conditioner including a plurality of compressors and a plurality of evaporators provided in rooms, the compressor starts or stops repeatedly because of variation of the air-conditioner load, the amount of oil in each of the compressor increases or decreases, and a large amount of refrigerant condenses when the compressor stops and at the low temperature. The compressor with a decreasing amount of oil easily goes wrong, and due to condensation of the refrigerant in the compressor, and not only a refrigeration cycle performance is reduced, in addition, a large amount of oil is also discharged when the compressor starts again.
In the present multi-connected air conditioner system, a plurality of the compressors are connected in the refrigeration cycle in parallel, and a method of the oil discharged by the compressor being recycled into an oil separator and returning to the low-pressure path, as well as a method of managing the amount of oil in the compressor by means of an oil level sensor and giving and receiving lubricating oil when necessary are spread in some extent. The management and control of the refrigeration cycle are complicated, and further problem of a low efficiency of the refrigeration cycle exists.